title: Nucleocytoplasmic shuttling of IPAS by its unique nuclear import and export signals unshared with other HIF-3α splice variants.
abstract: Inhibitory Per/Arnt/Sim (PAS) domain protein (IPAS) is a splice variant of hypoxia-inducible factor (HIF)-3α, and possesses two entirely different functions. One is as a transcriptional repressor against HIF-dependent hypoxic gene activation. The other is as a pro-apoptotic factor by direct binding to the pro-survival protein Bcl-xL and its related proteins on mitochondria. Presently, the regulatory mechanism that determines the intracellular distribution of IPAS to fulfill each of the two functions is unknown. As a first step towards elucidation of the mechanism, nucleocytoplasmic transport signals of IPAS were explored. A bipartite-like nuclear localization signal (NLS) was found in the N-terminal region by the deletion and mutation analysis of EGFP-IPAS. In addition, the helix-loop-helix domain showed weak nuclear import/retention activity. A leptomycin B-sensitive nuclear export signal (NES) was localized in the C-terminal region of the protein. A proline-rich region supported the NES activity. These NLS and NES are not carried by the other variants of HIF-3α due to differential exon usage. These results strongly suggest that IPAS is a nucleocytoplasmic shuttling protein.
authors.affiliation: Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Torii
authors.forename: Kohei
authors.initials: K
authors.lastname: Sakaki
authors.forename: Miki
authors.initials: M
authors.lastname: Otomo
authors.forename: Kyohei
authors.initials: K
authors.lastname: Saka
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Yasumoto
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Sogawa
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000235:genetics; D017398:Alternative Splicing / Q000235:genetics*; D051017:Apoptosis Regulatory Proteins; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics*; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D057809:HEK293 Cells; D006367:HeLa Cells; D018257:Helix-Loop-Helix Motifs / Q000235:genetics; D006801:Humans; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins
chemical_list: D051017:Apoptosis Regulatory Proteins; D051792:Basic Helix-Loop-Helix Proteins; D019913:Nuclear Localization Signals; D012097:Repressor Proteins; C116973:HIF3A protein, human
keywords: CRM1; IPAS; NES; NLS; hypoxia-inducible factor